The invention relates to a circuit for the field deflection in a picture display device suitable for receiving and processing a signal comprising line and field pulses, the field deflection circuit comprising a sawtooth generator, a power amplifier coupled to the sawtooth generator, and a field deflection coil connected to an output of the amplifier, and a clock pulse generator for applying clock pulses to the sawtooth generator, the sawtooth generator, for generating an essentially sawtoothshaped signal, being provided with a storage element for storing information under the influence of applied clock pulses and having reset means for resetting the storage elements under the influence of field pulses.
A circuit of this type is known from British patent application 2,095,491. In this known circuit an essentially sawtooth-shaped signal is generated wherein charges are applied to a capacitor as a result of the occurrence of clock pulses and wherein under the influence of a field-frequency reset pulse, the charge level is each time reduced to a given value. In fact, a staircase-shaped signal is generated but the sawtooth shape required for the vertical deflection is obtained in that the height of the separate steps is very small as compared with the total amplitude of the stair-case and in that smoothing means are used. Since the number of charges per field period has a predetermined value, the amplitude of the generated voltage is constant.
The known circuit also includes a phase control loop for controlling the frequency of the clock pulse generator. If the field frequency in the incoming signal changes, the control loop adjusts itself after some time in such a manner that the clock pulse frequency is a multiple of the field frequency while the amplitude of the sawtooth remain unchanged. In view of the very low value of the field frequency, such a control is, however, very slow and may give rise to instability at the instant of change. In addition, the control loop includes capacitors having a large capacitance which are not integratable in an integrated circuit. In an integrated circuit having most components of the circuit, a plurality of connection terminals must be reserved for this purpose.